The development of drug resistance often results in treatment failure in a variety of infectious organisms and this is of particular importance in pathogenic fungi where increased expression of multidrug efflux pumps is observed in drug-resistant clinical isolates. The baker's yeast Saccharomyces cerevisiae has served as an excellent model system for the study of both antifungal resistance and chromatin-based gene regulation. In this proposal, I will bring together these two areas of research to test the hypothesis that histone modifications play an important role in the regulation of genes that are involved in multidrug resistance (MDR). I propose to do this by using strains where either the major activation-correlated histone modification sites are mutated or have deletions in the histone modifying enzymes; I will test for changes in susceptibility to a variety of inhibitors and for defects in the expression of genes that encode for important multidrug efflux proteins. Using a novel genetic screening method that we have developed, I will attempt to identify positive and negative regulators of the gene encoding the Pdr5 drug efflux pump and confirm these interactions with the promoter by chromatin immunoprecipitation. Lastly, I will delete genes that encode histone modifying enzymes in the opportunistic pathogen Candida glabrata to determine if these regulatory systems also control drug susceptibility and MDR gene expression. The data that are generated from this initial research proposal may prove useful for understanding the control of MDR genes and reveal novel drug targets for antifungal therapy. These mechanisms can then be studied directly using medically important opportunistic fungi such as other Candida species and Aspergillus species in future proposals. [unreadable] [unreadable]